Smoking sends nicotine to the brain in a few seconds. Nicotine causes the brain to release dopamine (dope-a-meen). Dopamine is a chemical in the brain that makes you feel calm. Between cigarettes, the level of dopamine drops. Then, you start getting crabby and jumpy. Your brain craves nicotine to release more dopamine. Smoking again sends nicotine to the brain in a few seconds.